U.S. Pat. No. 6,562,913 issued on May 13, 2003 and entitled “Process for Producing High Vinylidene Polyisobutylene” (hereinafter the '913 patent) relates, inter alia, to liquid phase polymerization processes for preparing low molecular weight (number average molecular weight (MN) less than about 10,000), highly reactive (terminal double bond content of at least about 70%) polyisobutylene products. In accordance with the disclosure of the '913 patent, a catalyst composition, which desirably may comprise a complex of BF3 and complexing agent such as methanol, and a feedstock containing isobutylene, are each introduced into a reaction zone where the same are intimately admixed with residual reaction mixture so as to present an intimately intermixed reaction admixture in the reaction zone. The intimately intermixed reaction admixture is maintained in its intimately intermixed condition and at a relatively constant temperature of at least about 0° C. while the same is in the reaction zone, whereby isobutylene therein is polymerized to form a polyisobutylene product having a high degree of terminal (vinylidene) unsaturation. A crude product stream comprising residual catalyst composition, unreacted isobutylene and polyisobutylene is then withdrawn from the reaction zone.
The introduction of feedstock into and the withdrawal of product stream from the reaction zone are each controlled such that the residence time of the isobutylene undergoing polymerization in the reaction zone is no greater than about 4 minutes, whereby the product stream contains a highly reactive polyisobutylene product. Preferably, the reaction zone may be the tube side of a shell-and-tube exchanger in which a coolant is circulated on the shell side. A recirculation loop may desirably be employed to circulate the reaction admixture through the tube side reaction zone at a linear velocity sufficient to establish and maintain an intimately intermixed condition in the admixture and remove heat generated by the exothermic polymerization reaction.
U.S. Pat. No. 7,037,999 issued on May 2, 2006 and entitled “Mid-Range Vinylidene Content Polyisobutylene Polymer Product and Process for Producing the Same” (hereinafter the '999 patent) describes, inter alia, mid-range vinylidene content PIB polymer products and processes for making the same. In accordance with the disclosure of the '999 patent, at least about 90% of the PIB molecules present in the product are polyisobutylene isomers having either alpha or beta position double bonds. The alpha (or terminal) position double bond (vinylidene) isomer content of the product may range from 20% to 70% thereof, and the content of tetra-substituted internal double bonds is very low, preferably less than about 5% and ideally less than about 1-2%. The mid-range vinylidene content PIB polymer products are desirably prepared by a liquid phase polymerization process conducted in a loop reactor similar to the reactors described in the '913 patent at a temperature which desirably may be about 60° F. or higher using a BF3/methanol catalyst complex and a contact time of no more than about 4 minutes.
U.S. Pat. No. 6,992,152 issued on Jan. 31, 2006 and entitled “Apparatus and Method for Controlling Olefin Polymerization process” (hereinafter the '152 patent) relates, inter alia, to methodology for controlling the operation of reactors such as those described in the '999 and '913 patents so as to achieve efficiencies in process operation and better uniformity of the product of the process. In particular, the '152 patent describes methodology for controlling the ratio of BF3 to catalyst composition to thereby control the reactivity (terminal double bond content) of the product. Specifically, such control is achieved by providing for introduction of a catalyst modifier separately from the introduction of the catalyst composition itself.
U.S. Pat. No. 6,844,401 issued on Jan. 18, 2005 and entitled “Apparatus for Preparing Polyolefin Products and Methodology for Using the Same” (hereinafter the '401 patent) relates, inter alia, to procedures, etc. for improving the processes described above. In particular, the '401 patent describes an olefin reactor system that includes at least two separate reactor zones operating in parallel. Such multiple reactor system provides process efficiencies and advantages particularly in connection with conversion rates and polymer polydispersity. In addition, the '401 patent describes downstream systems for quenching the residual catalyst leaving with the crude product to quickly prevent further reaction, for removal of catalyst residues by washing, and for separation of the product from unreacted monomer, dimers, oligomers and other undesirable contaminants such as diluents and the like.
In accordance with certain of the preferred embodiments of the '913, '999, '152 and '401 patents, polyisobutylene products may be manufactured by processes comprising liquid phase polymerization conducted in a loop reactor at a temperature ranging from 30 to 90° F. The preferred catalyst may be a BF3/methanol catalyst complex and the reactor residence time may usually be no more than about 4 minutes. One of the preferred products may be a relatively low molecular weight, mid-range (50-60%) alpha position (vinylidene) double bond content PIB polymer. At least about 90% of the PIB molecules present in the product are either alpha position (vinylidene) double bond or beta position double bond isomers. The other polyisobutylene isomers produced generally may comprise less than 10% and ideally less than 5% of the molecules.
Table 1 set forth below shows possible isomer structures that might be found in low molecular weight polyisobutylene products. Other isomers may possibly be included in minor amounts and should not affect the overall reactivity of the PIB molecule.
In general, the reactivity of an olefinic double bond is directly related to its degree of substitution. That is to say, the more highly substituted the olefinic double bond, the less reactive it is. Therefore, since Structure I (alpha position or vinylidene double bond) of Table 1 is only disubstituted, it is much more reactive than Structures II, III or IV where the double bond is in a beta position. Structures II and III are both 1,2,2 trisubstituted and are less reactive than Structure I, but because there is an available hydrogen on the terminal carbon, they are more reactive than Structure IV which is 1,1,2-trisubstituted with no terminal hydrogen. Structure V is tetra-substituted and is the least reactive of all the depicted isomers.
Generally speaking, PIB products produced in accordance with the processes described in the '913, '999, '152 and '401 patents discussed above contain mainly Structures I and IV with the other isomers being present in only minor concentrations. Highly reactive (HR) polyisobutylene products (see the '913 patent) may generally contain about 80-85 mole % of Structure I (alpha position double bond) and about 15-20 mole % of Structure IV (beta position double bond). Mid-range vinylidene content PIB polymer products (see the '999 patent), which may sometimes be referred to as “enhanced” products, also are generally predominantly comprised of only Structures I and IV, but generally in a ratio of about 55-60 mole % of Structure I and about 35-40 mole % of Structure IV, respectively, with minor concentrations of the other oligomers.
TABLE 1Structures of PIB Isomers    
The '913, '999, '152 and '401 patents discussed above are each assigned to the assignee of the present application, and the entireties of the respective disclosures thereof are specifically incorporated herein by this reference thereto.
In conducting the processes described above, highly specialized equipment and procedures may often be utilized to enhance the operation and control of the polymerization reactions that are involved. Moreover, as in any industrial activity, methodology and/or equipment for enhancing capacity and throughput are sought continually. In particular, it is often very important in production of polyisobutylene to be able to carefully control (optimize) the rate at which the isobutylene is converted to polyisobutylene (conversion rate). It is also highly important in many cases to be able to carefully control (optimize) the polydispersity index (PDI) and/or the number average molecular weight (MN) of the polyisobutylene product. Even more importantly, it is extremely valuable in many commercial applications to be able to carefully control the concentration of reactive (terminal) double bonds in the polyisobutylene product.